Field of the Disclosure
The present disclosure relates to fixing apparatuses mounted to image forming apparatuses such as electrophotographic copying machines and electrophotographic printers.
Description of the Related Art
Film heating type apparatuses are known as fixing apparatuses mounted to electrophotographic copying machines and printers. This type of fixing apparatus includes a plate-like heater, a rotatable cylindrical film which is heated by the heater, and a holder that supports the rotation of the film. The fixing apparatus further includes a pressure roller that forms a nip portion with the heater, with the film therebetween, and a pressure stay that presses the holder against the pressure roller. A printing material that carries an unfixed toner image is heated while being nipped and conveyed through the nip portion, so that the toner image is fixed onto the printing material.
Fixing apparatuses of film heating type are required to make the glossiness of a toner image carried by calendared paper or the like serving as a printing material uniform in a direction perpendicular to the printing-material conveying direction. Japanese Patent Laid-Open No. 2007-33552 discloses a fixing apparatus in which a protruding portion protruding toward a pressure roller from a sliding surface of a heater with respect to the inner surface of a film in a direction perpendicular to a printing-material conveying direction is provided, at the nip portion of the holder, downstream from the heater in the printing-material conveying direction.
In the fixing apparatus of Japanese Patent Laid-Open No. 2007-33552, heat-resistant resin is used as the material of the holder in consideration of smoothness and wear because the holder rubs against the film. The holder is pressed by a metal pressure stay with higher rigidity to apply pressure to the pressure roller via the heater to thereby maintain a predetermined nip shape.
In the fixing apparatus of Japanese Patent Laid-Open No. 2007-33552, when the film rotates along with the rotation of the pressure roller, the holder receives a force from the film in the printing-material conveying direction, and the pressure stay receives a force in the printing-material conveying direction via the holder.
The fixing apparatus of film heating type is configured such that both ends of the pressure stay and the holder are supported by flanges for restricting the movement of the film in the direction perpendicular to the printing-material conveying direction. Therefore, when the pressure stay received a force in the printing-material conveying direction, the displacement amount (deflection amount) in the printing-material conveying direction is larger toward the center than at both ends of the pressure stay. At that time, the holder tends to increase in displacement amount in the printing-material conveying direction toward the center as compared with both ends of the holder according to the displacement amount of the pressure stay.
In such a case, the effect of the protruding portion of the holder is insufficient at the center of the holder. This may impair the glossiness of the toner image. This may also cause a difference in glossiness between the center and the ends of the holder, impairing the uniformity of the glossiness of the toner image.